The field of this invention is a method and device for removing thrombus from the peripheral or coronary vascular system and particularly from saphenous vein grafts (SVG) that were grafted during coronary artery bypass surgery.
Saphenous veins, which are large leg veins, are extracted and implanted to bypass diseased arteries in the surgical procedure of coronary artery bypass graft (CABG). Although saphenous vein grafts usually extend the life of the patient and improve the quality of life, these results endure for only a limited time. Saphenous vein grafts will frequently develop flow restrictions after about 8 years. When these restrictions occur, they are the result of both atherosclerosis and thrombosis.
There is no current well-accepted procedure for removing the thrombus, which sometimes extends the entire length of the SVG or is formed as thrombus segments within the SVG. The degree of organization of the thrombus in the SVG is greatest at its anastomoses or at the ends of the thrombus segments, and in these locations the thrombus is better organized and thus more resistent to removal. It is highly desirable that the thrombotic material that occupies the lumen of the SVG vessel be removed prior to invasive treatment of the underlying stenotic lesion. The thrombosis that occurs and finally stagnates the blood flow is the direct effect of the slowed velocity of the blood flow due to the stenosis.
When an SVG becomes clogged, there are two therapeutic options available: add an additional graft using the other saphenous vein (when available), or remove the thrombus with chemical thrombolytic drugs or vacuum extraction and treat the clogged vessel with therapies such as stents or balloon angioplasty. Because the SVGs are very fragile, these therapeutic methods have had severe limitations in the past.
The disadvantage of using a chemical thrombolytic drugs is their very slow dissolution rate, requiring the patient to be non-ambulatory and retained in intensive care during the systemic use of the thrombolytic drugs. The worst of the many complications may be cerebral bleeding. Additionally, the patient may be required to remain in a prolonged unstable state during a life-threatening period.
Vacuum extraction catheters, on the other hand, require the use of very large catheters having very large bores and diameters. These large sizes are dictated by the propensity of the blood and the thrombus to coagulate and block the lumen of the extraction catheters. Additionally, this method removes a large amount of blood during the process of extracting the clot.
When a thrombus originally forms in the coronary arteries, it has high viscosity fluid components with a minimal fibrous matrix contained in the fluid. The fibrous matrix tends to structurally bind the thrombus together; however, it can be easily separated.
In comparison, thrombus occurring in nonpatent saphenous vein grafts will tend to be more organized at the anastomotic sites or at the two ends of the thrombus segment and be relatively less organized within the centers. Within this relatively less organized matrix there will also be organized particles.
The problem of thrombosis is also present in the arterial vascular; however, the volume and degree of organization vary according to location. Thrombosis formed in coronary arteries is much smaller in volume and less organized. The peripheral and cerebral vascular systems also have varying degrees and amounts of thrombotic and stenotic occurrence. The thrombotic occurrence in larger vessels frequently will have a characteristically large and organized thrombotic deposit near a stenotic site.
Several approaches have been tried for removing obstructions and thrombus in the vascular. An early approach is recorded in the British Medical Journal in 1907. Dr. W. Sampson Handley passed a flexible tube into the femoral artery, connected the proximal end to an aspirator, and removed soft blood clots. He also introduced a ureteral catheter along the common femoral, the external iliac, and the common iliac artery until it reached the bifurcation of the abdominal aorta. Handley then sent a forcible stream of saline through the catheter to dislodge clot that returned through the divided end of the profunda.
Another approach for removing obstructions can be found in U.S. Pat. No. 5,114,399, which discloses a catheter for removing obstructive material from a body cavity or lumen. The invention of this patent is a catheter device and method for removing obstructive material using a high-speed rotating blade assembly that is forced into contact with the obstructive material and a homogenizing means that functions to disintegrate the cored material so that it can be aspirated away. This catheter has a blade assembly that rotates at 5,000 R.P.M. and that includes a cylindrical-shaped coring blade that cores into the obstructive material and homogenizing blades that dice the cored material into smaller pieces. Assuming that the blade assembly has an outer diameter of 0.04 inches, then the outer surfaces of the knife blade apparatus have a speed of over 700 inches per second. The cylindrical-shaped portion of obstructive material is forced through the cylindrical passage defined by the coring blade. The rotating blade assembly also includes diametrically extending blades that homogenize the obstructive material which is then aspirated out of the cylindrical passage. Irrigation fluid is pumped to the tip of the catheter through one lumen and aspirated out along with the homogenized material through another lumen. The high speed rotating blade assembly is in contact with the patient's blood stream.
In the '399 device fluid is in contact with high-speed moving components that could cause the blood in the proximity of the catheter to undergo hemolysis due to the localized shear stresses and the mixing due to induced fluid vortexing. Hemolytic effects in the fluid retained within the body of the surgical device would be of no consequence, but any lysed blood remaining in the circulatory system may result in thrombogenesis within the vascular of that or other organs of the body. The '399 device is designed for accessing and removing atheroma or obstructive materials, particularly stenotic materials, which are present behind the intimal layer of the vessel. Removal of the intimal layer is opposite the objective of the thrombus extraction device described as the device and method of this invention.
U.S. Pat. No 4,979,951 discloses an atherectomy device for removing atheroma in an arterial vessel. The device includes a longitudinal housing having a cutout extending longitudinally on one side of the housing. Within the housing there is a rotating cup-shaped cutter that can be advanced along the length of the housing. An inflatable balloon is secured to the housing on the side opposite the cutout such that when the balloon is inflated the cutout is forced against the wall segment containing the atheroma that is to be removed. When the cup-shaped cutter is filled with material from the atheroma, the atherectomy device is removed from the patient and then replaced if more material is to be removed. The invention of the '951 patent involves pressing the open-sided housing against the side of the blood vessel to isolate the atheroma being removed from its environment. The device is not directed to the task of removing thrombus but rather to removing atheroma which presents different problems and requires solutions different than that presented in this current application. The disadvantage of this system is that the cutter is exposed to the vessel wall and removes a portion of the intima layer in order to remove the atheroma formed therein. In addition, once the cutter cup is full, the device must be removed and emptied before continuing with the procedure.
For the foregoing reasons there is a need for a device and method for removing thrombus from saphenous vein grafts or from peripheral or coronary arteries at a controlled rate with a device that quickly removes thrombus but does not remove the intimal layer of the vessel wall, that does not expose the vessel wall directly to cutters, that does not have to be removed during the thrombus extraction procedure, and that does not clog.